Heating Element

WHAT GENERATES HEAT  in a heating element, is it high resistance or high current ? 

We know that it's the resistance that allows the material to generate heat. But that's not what the case is. What generates heat is the current flowing through the element, not the amount of resistance it has. Maximum current flowing through a heating element is much more important than forcing that current through a large resistance. This might seem confusing and counter-intuitive, but it's quite easy to see why it is (and must be) true.

Suppose you made the resistance of your heating element as big as you possibly could—infinitely big. Then Ohm's law (voltage = current × resistance or V = IR) tells us the current flowing through your element would have to be infinitely small (if I = V/R, I approaches zero as R approaches infinity). there will be a whopping great resistance, no current, and therefore no heat produced. Right, so what if we went to the opposite extreme and made the resistance infinitely tiny. Then we'd have a different problem. Although the current I might be huge, R would be virtually zero, so the current would zip through the element like an express train without even stopping, producing no heat at all.

We can reach exactly the same conclusion with math. The power produced or consumed by a flow of electricity is equal to the voltage times the current (watts = volts × amps or P = VI). We also know from Ohm's law that V = IR. Eliminate V from these equations and we find the power dissipated in our element is I2R. In other words, the heat is proportional to the resistance, but also proportional to the square of the current. So the current has much more effect on the heat produced than the resistance. Double the resistance and you double the power (great!), but double the current and you quadruple the power (fantastic!). So the current is what really matters.


A typical heating element is usually a coil, ribbon, of strip of wire made from nichrome that gives off heat much like a lamp filament. When an electric current flows through it, it glows red hot and converts the electrical energy passing through it into heat, which it radiates out in all directions. Nichrome is an alloy (a mixture of metals and sometimes other chemical elements) that consists of about 80 percent nickel and 20 percent chromium (other compositions of nichrome are available, but the 80–20 mix is the most common). There are various good reasons why nichrome is the most popular material for heating elements: it has a high melting point (about 1400°C or 2550°F), doesn't oxidize (even at high temperatures), doesn't expand too much when it heats up, and has a reasonable (not too low, not too high, and reasonably constant) resistance (it increases only by about 10 percent between room temperature and its maximum operating temperature).




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